The present invention relates to an improved trigger device for starting a seat belt tightening device which rotates a winding shaft of a retractor in a seat belt retracting direction, or an air bag device which protects a passenger from shocks given in a car collision by expanding an air bag suddenly by filling the air with gas.
In recent years, for the purpose of protecting a passenger in an emergency such as in a car collision or the like, there has been used a passive restraint device such as a seat belt tightening device, an air bag device and other similar devices.
In the above-mentioned seat belt tightening device, for example, a piston is connected to one end portion of a cable-shaped member which is wound about a pulley mounted on a winding shaft of a retractor and, when a tension force is applied to the cable-shaped member by means of a thrust force caused by the expansion pressure of a gaseous matter acting on the piston slidably received in a cylinder, then the cable-shaped member drives and pulls the retractor shaft in a direction to wind or retract a webbing, so that the webbing extended over the passenger can be pulled in or retracted in an emergency. Therefore, in the case of the seat belt tightening device, there is included a gas generator which is used to act on the piston provided within the cylinder to thereby apply a tensile force to the cable-shaped member. The gas generator contains therein an ignition heater and powder. In particular, the gas generator energizes the ignition heater electrically in response to a signal from a collision sensor and allows the powder to be ignited due to the heat that is generated by the ignition heater, thereby generating a gas.
Referring to the above-mentioned air bag device, for example, a module comprising a center pad, a folded air bag, a gas generator and the like is stored in a steering wheel. In a car collision, the gas generator is ignited to burn a gas suddenly and the air bag is instantaneously expanded by the suddenly burnt gas, whereby the body of a passenger is received by the expanded air bag to thereby be able to minimize the shock to the passenger. Therefore, in the case of the air bag device, there is included a gas generator which is used to supply an expansion gas for expanding the air bag. In particular, the gas generator ignites ignition powder to burn powder and then the powder is burnt suddenly to generate the expansion gas.
Accordingly, in the respective gas generators used in the above-mentioned seat belt tightening device and air bag device, a trigger device is required which, after a car collision is detected, ignites ignition powder to thereby operate the gas generators. And, as a sensor which is used to detect a collision, the trigger device of this type employs any of various sensors such as an electric sensor, an electronic sensor and a mechanical sensor.
The electric sensor is arranged such that, when an inertial member is moved a certain distance due to shock it closes a circuit, electrically energizes an ignition heater provided within the ignition powder of the gas generator, and thus ignites the ignition powder by means of the heat that is generated by the ignition heater. Also, referring to the function of the above-mentioned electronic sensor, it is the same as a generally used acceleration sensor. In other words, the electronic sensor simply outputs ever-changing accelerations as detect singles and the sensor itself does not judge a collision. That is, a control circuit, on receipt of the detect signals of the electronic sensor, analyzes the waveforms of vibrations caused by a collision to thereby judge the collision, and then energizes an ignition heater electrically. Further, referring to the mechanical sensor, similarly to the electric sensor, if a car collision occurs, then an inertial member is moved to remove a stopper mechanically, a trigger is caused to collide with a percussion cap provided in ignition powder due to the energizing force of energizing means which is removed from the stopper, and the ignition powder is thus ignited by the shock of the trigger.
However, in the case of the trigger device using the above-mentioned electronic sensor, car acceleration detect means such as an acceleration sensor or the like which detects the acceleration speed of a car and issues a detect signal, and a control circuit which judges in accordance with the detect signal whether the ignition heater may be electrically energized are required. This increases the number of parts used and complicates the structure of the start device. In addition to this, wiring for connecting the parts of the start device with one another must be connected positively to guarantee a system reliability, which worsens the assembling workability of the trigger device, resulting in an expensive system.
In the start device using the electric sensor, for example, in order to prevent the trigger device from being operated by other shocks, which may occur when a car body is hit by a hammer for repairing the car body, for example there are provided a plurality of sensors or the movement of the inertial member is braked by means of a viscous or resistance mertial. That is, the duration of the shocks is also added to the judgement elements to thereby prevent the start device from responding to pulse-like accelerations (the duration thereof is of the order of 2 ms.). However, in order to enhance the sensitivity of the electric sensor, there is required a high working accuracy and also there is increased the possibility of the malfunction thereof, which makes it difficult to change the acceleration detect characteristic of the sensor. As a result of this, the system provides only a small degree of freedom of design.
Further, in the case of the trigger device using the mechanical sensor, to ignite the percussion cap, the trigger must be moved somewhat greatly and at a high speed. For this reason, the trigger used to strike the percussion cap is provided separately from the inertial member which is used to sense the acceleration. As a result of this, the response time from the beginning of the movement of the inertial member to the ignition of the ignition powder is apt to be slower when compared with the start device using the electric sensor.